Objective：To explore a better tracing method of central lymph nodes in papillary thyroid cancer patients by comparing the numbers and staining rate of central lymph nodes between preoperative ultrasound-guided injection and intraoperative injection of nano-carbon. Methods：A total of 227 patients were randomly enrolled into preoperative ultrasoundguided injection group and intraoperative injection group. The rate of dye spillover，the numbers and staining rate of the lymph nodes in each sub-area of central region（linea alba cervical lymph nodes，prelaryngeal lymph nodes，pretracheal and paratracheal lymph nodes）were recorded and analyzed. Results：The proportion of nano-carbon spillover in precperative ultrasound guided injection was lower than that in the intraoperative injection group；while central lymph nodes，pretracheal and paratracheal lymph nodes were more in the preoperative injection group than in the intraoperative injection group（P＜0.05）. For patients with Hashimoto’s thyroiditis，with metastatic central lymph nodes accessed preoperatively，with a tumor diameter more than 1 cm，central lymph nodes were more accessible to be stained by preoperative injection of nano-carbon（P＜0.05）. Conclusion：Preoperative ultrasound guided injection of nano-carbon can reduce dye spillover and improve the staining rate and detection rate of central lymph nodes.